Multi-digit electrical combination lock



April 23, 1968 B. G. WATKINSON 3,380,024

MULTI-DIGIT ELECTRICAL COMBINATION LOCK Filed April 16, 1964 2 Sheets-Sheet l INVENTOI? B.G. WATKINSON April 23, 1968 5. ca. WATKINSON 3,380,024

MULTI-DIGIT ELECTRICAL COMBINATION LOCK Filed April 16, 1964 2 Sheets-Sheet 2 C 3 RC- 4 R F [:1 R2! s 1 RD-ALI EB 1.- l

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INVENTOR B. G. WAT K I N SON Cur'pfac y (fHckso A 6 EN 7' United States Patent 3,380,024 MULTI-DIGIT ELECTRICAL COMBINATION LUQK Brian G. Watkinson, Lasalle, Quebec, Canada, assignor to Northern Electric Company, Limited, Montreal, Quebec, Canada Filed Apr. 16, 1964, Ser. No. 360,398 Claims. (Cl. 340-464) ABSTRACT OF THE DISCLOSURE This invention relates to a circuit for actuating an electrical door lock in response to a preselected m digit code selected from a choice of n digits for a maximum of n codes. The circuit comprises n individual key circuits connected in parallel, each key circuit including a digit key and a resistor connected in series. Each digit key is connected to associated contacts of m rotary switches. The wiper of each rotary switch is connected to a relay. The relays are energizable in sequence to open the lock when all the digits of a preset code are correctly keyed within a predetermined interval.

The source of potential for operating the relays is a capacitor which is charged by a battery. The capacitor stores enough energy for operating a single relay at the time. This feature permits the utilization of the maximum number of codes because the combinations having two identical adjacent digits are available (e.g. 6113). In code 6113, for example the capacitor will not have enough energy to operate the relay associated with the second digit 1 in response to depression of the digit key 1. The digit key 1 will have to be released to recharge the capacitor before the relay associated with second digit 1 can be energized.

This invention relates to multi-digit electrical combination locks energized by an m digit code from a choice of 11 digits for a maximum of n codes.

It is generally conceded that multi-digit combination locks are more secure against being opened by unauthorized persons than are the usual key operated locks. The usual combination locks of the electrical type, however, are not entirely satisfactory as they rely on complicated mechanisms to insure a high level of security. The prior art shows various systems adapted to nullify any attempts at hunting for any one of the multi-digits of the assigned combination by actuating two or more pushbuttons together or in succession. For example, US. Patent 3,024,452 issued to Leonard on Mar. 6, 1962 uses a number of relays to insure that any attempt at digit transmission which fails to coincide with the currently assigned combination establishes a locked condition which disables the lock from opening and sounds an alarm. However, the Leonard and the other prior art systems are very complicated and expensive due to their large number of components.

It is also desirable that the maximum number of digit combinations be obtained for a given number of digits. This means that combinations having a repetition of the same digit must be available (e.g. 6113). In combinations where the same digit is repeated, some means must be provided to prevent energization of the relay associated with the repeated digit in response to actuation of the first pushbutton. The Leonard patent, for example, uses a number of interlocking contacts to ensure that the relay associated with the repeated digit will not be energized until the first actuated pushbutton is restored. This arrangement is cumbersome however and expensive due to the extra number of relays and contacts required.

These disadvantages of the prior art are overcome in accordance with the present invention, by using exponentially decaying pulses to operate the relays associated with each of the digits of a multi-digit electrical combination lock. The pulses have a discrete amount of energy which is just enough to operate a single relay. Consequently, not more than one relay can be operated at a time. It can readily be seen that by providing a source of power having a limited amount of energy, a large number of interlocking relays and contacts can be eliminated. In fact, the number of relays can be reduced to the number of digits of a predetermined code plus one relay to operate the lock. The number of contacts per relay is also greatly reduced.

It is also a feature of the invention to use a time-out circuit in conjunction with the combination lock of the invention to provide timing features essential for security reasons by preventing unlimited hunting for the correct combination.

In a multi-digit electrical combination lock, it is common practice to use a series of selecting switches which are set at contact positions corresponding to the digits of the desired code. A further feature of this invention is to provide an additional contact position for each switch whereby the effects of that switch may be nullified to erase that digit from the code.

The above mentioned and other features of this invention will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing in which:

FIG. 1 is a circuit diagram of a multi-digit electrical combination lock embodying the present invention; and

FIG. 2 is a circuit diagram of a transistorized time-out and alarm system used in conjunction with the combination lock of FIGURE 1.

A source of DC. voltage such as battery B charges capacitor C1 through a resistor R. Capacitor C1 is normally maintained at a predetermined potential by Zener diode Z. The capacitor is connected to the common side of a key set comprising ten keys (0-9). The keys are connected to ground through individual resistors R0 to R9. Each key is also connected to associated contacts (0-9) of four rotary switches 10 to 13. The common terminal of each of the rotary switches 10 through 13 is connected to relays RA, RB, RC and RD, respectively. Resistor R is chosen at a value large enough to prevent relays RA-RO from operating without capacitor C1.

Lock operation by coded keying The four digit code is selected by switching each of the four rotary switches 10 through 13 to any one of the available 10 contact positions (e.g. code 1336 in FIG. 1 of the drawings). Operation of the key corresponding to the first digit (1) of the code discharges capacitor C1 through rotary switch 10, relay RA and its preceding normally closed contacts RA-l, and the normally closed contact RF-3 of a relay RF (to be described hereinafter) thus operating relay RA. Once operated, relay RA locks in through its own contacts RA-Z connected to battery B. Relay RA also closes contacts RA-3 which partially prepares the operating path of relay RB.

Release of the first digit key recharges capacitor C1. Operation of the second digit key (3) discharges the capacitor C1 through rotary switch 11, now closed contacts RA-3, relay RB and its preceding normally closed contacts RB-l, normally closed contacts RD-3 and normally closed contacts RF-3 thus operating relay RB. Once operated relay RB locks in through its own contacts RB-2 connected to battery B. Relay RB also operates contacts RB-3 which partially prepares the operate path of relay RC.

Release of the second digit key recharges capacitor C1. Operation of the third digit key (3) discharges capacitor C1 through switch 12 to operate relay RC in a manner similar to relays RA and RB. Once operated, relay RC locks in through contacts RC-Z and partially prepares the operating path of relay RD by closing contacts RC-3.

Capacitor C1 recharges on release of the third digit key and is discharged by operation of the fourth digit key (6). The capacitor discharges through switch 13 to operate relay RD in a manner similar to relays RA, RB and RC. Once operated relay RD locks through its own contacts RD-Z. Relay RD also releases relays RB and RC by opening its normally closed contacts RD-S and supplies battery to solenoid S of the door lock magnet through contacts RD-4 (FIG. 2) thereby unlocking the door.

It is very important to note at this time that because of the discrete amount of energy stored in capacitor C1, relay RB alone will be operated by the actuation of the second digit of code 1336 even if key 3 is held down. Capacitor C1 is chosen at such a value that it does not contain enough energy to energize relay RC after contacts RB-3 are closed. The second digit key must he released to recharge capacitor C1 before relay RC can be energized.

Keying and alarm time-out periods As mentioned earlier, keying of the first digit of the code operates relay RA. The keying time-out period is initiated :by a ground on lead 20 applied by relay RA through contacts RA-4. The ground on lead 20 charges capacitor C2 through resistor R20. If the remaining digits of a code are not correctly keyed within a predetermined time interval, capacitor C2 will charge to a value sufliciently high to fire unijunction transistor Q, reducing its impedance. The current through transistor Q will then be sufiicient to operate relay RF. Operation of relay RF closes contacts RF-l to sound an alarm, and also opens contacts RF-3 to release all the operated relays in the code selection circuit and also remove the ground connection from lead 20 by reopening contacts RA-4.

If all the digits of a code are correctly keyed within the predetermined keying interval, the capacitor C2 is charged as before but relay RD opens contacts RD-S in the changing circuit of capacitor C2 before its potential reaches a value sufficiently high to operate transistor Q. Any accumulated potential on capacitor C2 is then removed by the connection of resistor R21 across the capacitor through now closed contacts RD-6 and RC-4. Resistor R21 shorts out capacitor C2 only momentarily since relay RD, when operated, releases relay RC to open the contacts R04 and allow capacitor C2 to recharge at a different rate as determined by resistors R20 and R23.

This new charging rate provides an alarm time-out period. When the potential across capacitor C2 once again reaches a value such that unijunction transistor Q becomes conductive, relay RF operates and releases relays RA, RB, RC and RD. If the door is still open when relay RF operates, a door switch 21 locks in relay RF through its contacts RF2 thereby sounding an alarm until the door is closed to open switch 21.

When the door is opened from the inside, the door switch 21 closes and connects ground to lead 20 over resistor R24. If the door remains open for a predetermined interval relay RF operates as before and locks in under control of the door switch. Contacts RF-l of relay RF operate the alarm until the door is closed and the door switch is restored to its normally open position.

It is understood that various time-out intervals could be obtained by varying of values of resistors R20, R23, R24 and capacitor C2.

Keying of non-coded digits Each code combination requires sequential key operations to unlock the door. At any instant there is only one correct digit to key, and the complete code combination must be keyed within the predetermined time-out period.

If in the keying sequence an incorrect digit is operated, the keying capacitor C1 will dischange through one of the ten resistors R to R9. If the key is released to allow capacitor C1 to recharge, and if the remaining digits of the code are operated correctly within the remaining keying time-out period, the door will unlock.

If, on the other hand, two or more digits are operated at the same time, capacitor C1 will not operate any of the relays associated with the corresponding digits because the discrete amount of energy stored in capacitor C1 will be shunted down by resistors R0-R9, leaving insufiicient energy to operate any relay.

Code and digit erasure Setting any of the rotary switches except the first to position 10 connects battery B to the common terminal of the rotary switch. Once the preceding digit is keyed and its relay operated, the rotary switch set to position 10 operates its associated relay automatically and thereby erases that digit from the code.

While a single practical embodiment of the invention has been set forth herein, it is to be clearly understood that this description is made only by way of example and that this invention is not to be limited to the details illustrated and described except in so far as those details may be defined in the claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A circuit for actuating an electrical door lock to unlock a door in response to a preselected m digit code selected from a choice of n digits for a maximum of n codes comprising:

(a) 11 individual key circuits connected in parallel each circuit comprising a digit key and an associated resistor connected in series;

(b) m digit selecting switches each having it inputs and one output, the first switch having each input connected to an associated key of said key circuits, associated inputs of the remaining switching being multiplied together, a code assigning means connecting a preselected input of each selecting switch to its output;

(0) m relays each connected to the output of an associated selecting switch, each relay and associated selecting switch being connected across said associated resistors, the energization of each said relay providing an energization path for the subsequent relay, the actuation of the m relay actuating the electrical door locks;

(d) and a source of discrete energy connected to said key circuits whereby each relay is energized when a key associated with a preselected code is actuated, said source of discrete energy being provided by exponentially decaying pulses having just enough energy to operate a single relay at a time whereby the same digit may be assigned to two selecting switches associated with two sequentially operated relays so as to provide the maximum number of codes available.

2. A circuit as defined in claim 1 in which said source of discrete energy is provided by the discharge of a DC. voltage built up across the terminals of a capacitor.

3. A circuit as defined in claim 1 in which the energization path of said relays includes the normally closed contacts of a time-out relay which deenergizes said relays by opening its contacts when the preselected code is not keyed Within a predetermined time interval.

4. A circuit as defined in claim 3 in which said timeout relay also includes normally open contacts which close and cause operation of an alarm when the preselected code is not keyed within a predetermined time interval.

5. A circuit as defined in claim 3 in which said timeout relay is included in the circuit of a unijunction transistor which is rendered conductive by a capacitor charged at a predetermined rate in response to energization of the first of the m relays.

6. A circuit as defined in claim 5 further including means for momentarily discharging said capacitor after the m relay is energized when the code is correctly keyed and for recharging said capacitor at a second predetermined rate, the full recharge of the capacitor causing the energization of the time-out relay and the release of the m relays.

7. A circuit as defined in claim 6 wherein said timeout relay has a holding circuit including a door operated switch, the holding of the time-out circuit causing the sounding of an alarm when the door is left open longer than a predetermined interval determined by said second predetermined rate of charge of the capacitor.

8. A circuit for actuating a door lock magnet to unlock a door in response to a preselected m digit code selected from a choice of 11 digits for a maximum of-n codes comprising:

(a) a source of discrete energy provided by exponentially decaying pulses;

(b) m interconnected relays, each of which provides an energization path for the subsequent relay, the actuation of the m relay actuating the door lock magnet;

(c) n digit keys having a common terminal connected to a first terminal of said source, each other terminal of said keys being connected to one terminal of an associated resistor, the other terminal of each resistor being connected in common to the other terminal of said source, a predetermined number m of said keys being operable in accordance with a pre-set code to sequentially energize each of said interconnected relays to release said door magnet, the exponentially decaying pulses having just enough energy to operate a single relay at a time, whereby codes having two identical adjacent digits for actuating two sequentially operated relays are available to provide the maximum number of codes;

(d) and m rotary switches each having a group of contacts corresponding to the n digit keys and being connected between said each other terminal of said keys and said relays, said switch being adjustable to change the pre-set code for operation of the door lock magnet.

9. A circuit as defined in claim 8 in which said source of discrete energy is provided by the discharge of a D.C. voltage accumulated across the terminals of a capacitor.

10. A circuit as defined in claim 8 in which said rotary switches include an additional contact, the additional contact of each rotary switch except the first one being connected to a power source whereby positioning of said switch on said additional Contact will automatically operate its associated relay once the preceding relay has been operated and thereby erase that digit from the code.

References Cited UNITED STATES PATENTS 2,677,814 5/1954 Miller 340-147 2,855,588 10/1958 Allen 317l34 XR 3,024,452 3/1962 Leonard 340--164 XR 3,242,388 3/1966 Tellerman 317134 3,308,432 3/1967 Gerry 3l7l34 XR JOHN W. CALDWELL, Primary Examiner.

DONALD J. YUSKO, Examiner. 

